Process for aldol condensation

ABSTRACT

Basic mixed oxides useful for base catalyzed reactions such as the aldol condensation of acetone and also useful as catalyst supports are made by mixing an acid such as nitric acid or acetic acid with a pseudoboehmite to form a gel, adding magnesium oxide or hydroxide, in a ratio of magnesium to aluminum of about 1:1 to about 10:1, agitating and heating for about 1 to 24 hours, and subsequently drying and calcining. The resulting polymorphic magnesium-aluminum oxide composition is hightly effective in the aldol condensation of acetone to isophorone, and other base catalyzed reactions such as isomerization of olefins, aldol condensation of aldehydes.

This is a division of application Ser. No. 339,745, filed Apr. 18, 1989now U.S. Pat. No. 4,970,191.

TECHNICAL FIELD

This invention relates to new catalysts, methods of making them, andcertain aldol condensations employing them. In particular, it relates toa method of making a catalyst or catalyst support whereby apseudoboehmite is peptized with an acid to form a dispersion or gel,which is then reacted with magnesium oxide; the material is then driedand calcined. The catalyst may be used for making mesityl oxide andisophorone from acetone.

BACKGROUND ART

Prior to the present invention, it has been known to prepare catalystsand catalyst supports from pseudoboehmite, particularly by calcinationof the pseudoboehmite to aluminum oxide or more specifically gammaalumina. Pseudoboehmite is a material of choice because of itsreactivity, availability and forming properties. This material is widelyused as a catalyst support and catalyst for many chemical processes.

However, a very particular property of pseudoboehmite derivatives isthat they are mainly acidic which is usually useful for catalyticreactions which involve carbo-cation intermediates, such as in alcoholdehydration, skeletal isomerization, ring alkylation, and cracking ofhydrocarbons. When they are used as supports, their acidity is usuallynecessary for activation of a catalytic agent such as nickel, platinum,or molybdenum in a bifunctional mechanism needed for the desiredreaction.

Prior to the present invention, it has been known to convert acetone toisophorone and mesityl oxide by condensation in the presence of acatalyst made by reacting (or "interacting") certain aluminum salts withcertain magnesium salts or hydroxides--see Reichle, U.S. Pat. Nos.4,165,339 and 4,458,026. A catalyst described as "Mg-Al-CO₃ HydrotalciteCatalyst" and similar compositions were proposed in the examples ofReichle's U.S. Pat. No. 4,458,026, using as ingredients such materialsas Mg(NO₃)2.6H₂ O and Al₂ (NO₃)3.9H₂ O together with sodium carbonate.Synthetic hydrotalcites (Joint Committee on Powder Diffraction Standardsfiles #14-191 and 22-700) sometimes also referred to as a magnesiumaluminum hydroxy carbonate are also proposed in U.S. Pat. Nos. 4,656,156and 4,476,324. Other similar catalyst compositions containing magnesiumand aluminum are disclosed in U.S. Pat. Nos. 4,539,195 and 4,086,188.Such compositions are not made from the mixed oxides of magnesium andaluminum, however, but generally begin with at least one salt orhydroxide, which affects the crystalline structure of the finalcomposition. The method of "interacting" the salts has become known asthe co-precipitation method.

Various mixed oxides are reviewed in Papa's U.S. Pat. No. 4,535,187,which contains the statement (col. 1, lines 48-51) "The co-precipitatedmixed oxide catalysts have the drawback of exhibiting poor catalystmanufacturing reproducibility and are expensive." The review, however,does not include a discussion of a mixture of aluminum and magnesiumoxides.

DISCLOSURE OF INVENTION

The present invention differs from the above described various methodsof obtaining catalysts containing magnesium and aluminum in that itemploys a particular sequence of steps not heretofore described andobtains a catalyst composition different from those described in thepast.

In the present invention, pseudoboehmite is used as one of the maincomponents for the preparation of the catalyst. It is reacted withmagnesium oxide (or magnesium hydroxide) to form a mixed metal hydroxidewhich yields after calcination an oxide possessing strong basicproperties. Such properties are used to catalyze reactions viacarbanionic species. Typical base catalyzed reactions which can beconducted with my catalyst are double bond migration of olefins,side-chain alkylation of alkylaromatics, Michael reactions, Aldolcondensations, alkylation of phenol at the ortho-positions,oxygen-sulfur-nitrogen interchange reactions, polymerization of lactonesand decomposition of methyl formate.

In the examples and discussion below (and throughout this application)pseudoboehmite means small crystallites of Boehmite or AlOOH having anX-ray diffraction pattern corresponding to the JCPDS file #21-1307.Broad X-ray lines are characteristic of the crystallites size of thismaterial. Pseudoboehmite has the property of being dispersed with acidinto colloidal particles (positively charged particles having sizes lessthan one micron in diameter) but not of being soluble in dilute acid.This material is commercially available under the name of VERSAL,CATAPAL, PSEUDOBOEHMITE, or DISPERAL. I prefer to use acetic acid, butany water soluble organic or inorganic acid can be used.

More specifically, I have found that I may begin with a pseudoboehmiteor an amorphous gel of aluminum hydroxide, mix it with, approximately,an equivalent of an inorganic or organic acid to form a gel, and permitthe gel to react with MgO for at least about 1 hour. Calcining of theresulting material is critical--it should be calcined preferably atabout 300 to about 500 degrees Centigrade for about 1 hour to about 18hours. Even though the initial treatment of pseudoboehmite with an acidresults in a composition which may be called a gel, the reaction of thepseudoboehmite with MgO is a reaction of two solids. The gel may also bereferred to as a dispersion of pseudoboehmite crystallites, that is, ofsmall crystals of pseudoboehmite.

A general method for the preparation of the materials includes thefollowing steps described hereafter.

Pseudoboehmite and an acid solution are mixed together, which results inthe formation of a sol or gel. The quantities of acid and pseudoboehmitecorrespond to a atomic ratio of Al/proton between about 0.2 and about 4but preferably between about 0.8 and about 1.2.

Magnesium oxide is added to the pseudoboehmite slurry in a magnesium toaluminum ratio of about 1:1 to about 10:1, preferably of about 2:1 toabout 3:1, and is allowed to react for a period of time between 1 and 24hours. Heating the reaction mixture is not necessary but will improvethe reaction rate. The course of the reaction can be followed by theexothermicity of the reaction and the disappearance of the crystallinemagnesium oxide. Moreover, the reactivity index of magnesium oxide(which is related to the crystal size) is not critical; surface areas ofMgO lower than 1 m² /g, which corresponds to a very low reactivity and avery slow hydration rate are preferred. The product at this stage of thepreparation is a homogeneous thick slurry which is relatively easy tofilter. X-ray diffraction patterns recorded on dried samples show thepresence of an ill-defined phase which has a layer structure similar tothe naturally occurring hydroxy-carbonates described by R. Allman (Am.Min., 53, 1057-59). However, no carbonates are used or found in thesynthetic hydroxides made by the above procedure.

Calcining the dried hydroxide in air or inert atmosphere at about 300°to about 500° C. for about 1 to about 24 hours.

As known in the art, many compounds of the elements of the periodictable can be added during any of the steps described above, either aspromoters, co-catalysts or catalytic agent. It is also understood thatother preparation steps can be added to the above general procedure. Forinstance, treatment with hydrogen, oxygen or hydrogen sulfide may beused to make a specific catalyst or catalyst support within the scope ofthis invention.

At any time after filtration, it is also understood that the materialcan be shaped in various forms by extrusion, spray-drying orcompression. Also, the wet product can be deposited as a washed-coat onmonoliths or honeycombs of other materials. My catalyst composition isof course effective by itself for various purposes as is describedherein and also may be used as a support for other catalytic materials.

FIG. 1 in the drawings is an X-ray diffraction pattern (Cu kα) ofmagnesium oxide used as reagent in Example 2.

FIG. 2 is an X-ray diffraction pattern (Cu kα) of the pseudoboehmiteused as the reagent in Example 2.

FIG. 3 is an X-ray diffraction pattern (Cu kα) of the dried intermediateproduct of Example 2, before calcination, and

FIG. 4 represents an X-ray diffraction pattern (Cu kα) of the sameproduct calcined at 450° C. for one hour. In each figure, the X-axisrepresents 2θ and A.

BEST MODE FOR CARRYING OUT THE INVENTION

Following are examples of the preparation and use of the catalyst:

EXAMPLE 1

This example describes a preparation of the catalyst. 81.6 g of glacialacetic acid was added to a slurry containing 89 g of pseudoboehmite("Versal 850") and 200 ml of deionized water, the mixture beingcontinuously agitated. After 30 minutes approximately, 2 liters ofdeionized water and 57.6 g of magnesium oxide (Magchem 10-325 fromMartin Marietta) were added and the resulting mixture was continuouslyagitated and heated to 85°-95° C. for 7 hours. This amount of magnesiumoxide corresponds to a Mg/Al atomic ratio of 2.6. The white digestedsolid was then filtered and dried at 110° C. The dried solid was groundand sieved to 30-16 Mesh and calcined at 400° C. for 5 hours in a mufflefurnace.

EXAMPLE 2

200 ml of deionized water was introduced with 35 g of pseudoboehmite("CATAPAL") in a 6 liter glass Erlenmeyer flask. With continuousagitation, 50 g of concentrated nitric acid (70 wt % HNO₃) was slowlyadded to the alumina slurry, causing the formation of a thick colloidalgel. These quantities of acid and pseudoboehmite correspond to amilliequivalent ratio of Al/anion of about 3.

After 30 minutes, 2 liters of deionized water and 57.6 g of magnesiumoxide were added and the resulting mixture was continuously agitated andheated to 85°-95° C. for 7 hours. This amount of magnesium oxidecorresponds to a Mg/Al mole ratio of 2.6. The white digested solid wasthen filtered and dried at 110° C. The dried solid was ground and sievedto 30-16 Mesh and calcined at 450° C. for 60 minutes.

FIG. 1 shows the X-ray pattern (Cu kα radiation) of the MgO; FIG. 2shows that of the AlOOH, and FIGS. 3 and 4 show those of the resultingformed material before and after calcination. The dried product wasidentified as a mixed metal hydroxide having a layered brucite-likestructure similar to the mineral Hydrotalcite (Joint Committee on PowderDiffraction Standards files #14-191 and 22-700). However, the nitrateanions substitute carbonate anions of the mineral which results indifferent basal spacings (d003-8.07 instead of d003-7.84). Also, someunreacted pseudoboehmite was detected in the X-ray pattern.

After calcination, the hydrotalcite phase was totally decomposed and atypical X-ray pattern showed the presence of a solid solution ofMagnesium-aluminum oxide similar to the structure of periclase (MgO).

A typical X-ray pattern of the catalyst is defined by the presence oftwo major diffraction peaks having a d-spacing of about 2.099±0.2 Å and1.490±0.2 Å as shown in FIG. 4.

EXAMPLE 3

81.6 g of glacial acetic acid was added to a slurry containing 89 g ofpseudoboehmite (VERSAL 850) and 200 ml of deionzied water. The gel waswell homogenized and 3 liters of water added while the mixture wascontinuously agitated and heated to 70°-80° C. for one hour. 5 liters ofwater were then added together with 105 g of magnesium oxide. Themixture was stirred and heated at 80°-90° C. for 18 hours. The pH of thecooled suspension was 8.3. The resulting gel was then dried at 110° C.and calcined at 350° C. for 5 hours.

EXAMPLE 4

In order to demonstrate that the catalyst can be used for base catalyzedreactions, a calcined sample of Example 1 has been used to isomerize1-butene to cis and trans-2-butene. 1 g of material of Example 1 wasintroduced into a 1/8" tube and a mixture of nitrogen and 1-butene in avolume ratio of about 1:1 was passed through at a flow rate of 30ml/min. and a temperature of about 150° C. The outlet gas was analyzedby gas chromatography and was found to contain 85.5 % 1-butene, 2.8 %trans-2 butene and 11.6 % cis-2 butene. The ratio cis/trans of 4.1 isconsistent with a base catalyzed mechanism.

EXAMPLE 5-7

In order to demonstrate that the catalyst is an effective catalyst forthe aldol condensation of ketones, a sample of the catalyst prepared byexample 2 was used to condense acetone to mesityl oxide and isophorone.The reaction was carried out in a 3/4" tubular reactor of 316 stainlesssteel and loaded with 35 g of extruded catalyst. The height of the bedwas 8.5 inches. The tests were conducted at 300°, 325° and 350° C. andthe feed rate of acetone was adjusted to 40, 104 and 160 ml/hourrespectively in order to obtain 30% conversion. The conditions andresults of the tests are shown in the table below. Selectivities ofmesityl oxide and isophorone were as high as 87% which shows that thecatalyst can be used with high efficiency for the aldol condensation ofacetone.

    ______________________________________                                                        Ex: 5  Ex: 6    Ex: 7                                         ______________________________________                                        Reaction conditions:                                                          reaction temperature                                                                            300° C.                                                                         325° C.                                                                         350° C.                            acetone feed rate (ml/hour)                                                                      40      104      160                                       nitrogen flow (ml/min.)                                                                          40       23       23                                       pressure (PSIG)    15       15       15                                       Wt % of reactor effluents:                                                    acetone            70.4     69.6     67.2                                     mesityl oxide      3.7      3.1      3.2                                      isophorone         17.8     18.9     20.4                                     high boiling products                                                                            4.9      5.1      5.5                                      Conversion (wt %)  29.6     30.4     32.8                                     Selectivities (wt %) (dry basis)                                              mesityl oxide      14.8     12.3     11.8                                     isophorone         72.6     74.7     74.5                                     others             12.6     13.0     13.7                                     Total selectivity  87.4     87.0     86.3                                     mesityl oxide + isophorone                                                    ______________________________________                                    

Temperature may be adjusted between about 200° C. and 400° C. or higher,preferably 275° C. to 350° C., with various residence times and/or feedratio as is known in the art.

EXAMPLE 8-9

The stability of the catalyst was tested for the aldol condensation ofacetone with catalysts of example 2 (using nitric acid) and example 1(using acetic acid). The conditions and results of the experiments areshown in the table below.

    ______________________________________                                                      Example 8 -                                                                             Example 9 -                                                         Catalyst of                                                                             Catalyst of                                                         Example 2 Example 1                                             ______________________________________                                        Reaction conditions                                                           catalyst bed    3/4 × 28 in.                                                                        1/2 × 25 in.                                dimensions                                                                    catalyst charge 104 g       40 g                                              pressure        15 PSIG     15 PSIG                                           acetone feed rate                                                                             130 ml/hour 130 ml/hour                                       temperature profile                                                                           305-335° C.                                                                        273-304° C.                                Results obtained after 500 hours of reaction:                                 conversion (wt %)                                                                             42.9        24.6                                              selectivities (wt %)                                                          mesityl oxide    7.6        15.5                                              isophorone      71.5        72.9                                              others          20.9        11.6                                              Results obtained after 1000 hours of reaction:                                conversion (wt %)                                                                             38.8        22.5                                              selectivities (wt %)                                                          mesityl oxide   10.0        18.1                                              isophorone      72.7        73.0                                              others          14.3         8.9                                              ______________________________________                                    

EXAMPLE 10

Aldol condensation of aldehydes has also been tested by condensingn-butyraldehyde to 2-ethyl-hexene-al. 1 g of catalyst of example 3 wasintroduced into a microreactor and the reaction was conducted at 150° C.Nitrogen was saturated at 35° C. with n-butyraldehyde in a saturator andpassed through the catalyst bed at a rate of 24 ml/min. The effluent ofthe reactor was analyzed by gas chromatrography and was composed of 77wt % unreacted n-butyraldehyde, 22 wt % of 2-ethyl-hexene-al and 1% ofunknown products. The selectivity of condensing the aldehyde to itsdimer was 99%. This experiment shows that the catalyst is an effectivecatalyst for condensing aldehydes selectively.

I claim:
 1. The aldol condensation of a ketone conducted at temperaturebetween about 200° C. and about 400° C. in the presence of a catalystmade by a method comprising mixing a water-soluble acid withpseudoboehmite to form a dispersion of pseudoboehmite crystallites,adding MgO or Mg(OH)₂ in a ratio of Mg to aluminum in the gel of about1:1 to about 10:1, agitating the mixture until the MgO or Mg(OH)₂ hassubstantially disappeared, drying the mixture, and calcining it at about300° to about 500° C. for about 1 to about 24 hours.
 2. Aldolcondensation of claim 1 wherein the water-soluble acid is acetic acid.3. Aldol condensation of claim 1 wherein the water-soluble acid isnitric acid.
 4. Aldol condensation of claim 1 wherein the atomic ratioof magnesium to aluminum is between about 2:1 to about 3:1.
 5. Method ofmaking isophorone and mesityl oxide comprising condensing acetone atabout 200° C. to about 400° C. in the presence of a catalyst made bymixing a water-soluble acid with pseudoboehmite to form a dispersion ofpseudoboehmite crystallites, adding MgO or Mg(OH)₂ in a ratio of Mg toaluminum in the gel of about 1:1 to about 10:1, agitating the mixtureuntil the MgO or Mg(OH)₂ has substantially disappeared, drying themixture, and calcining it at about 300° to about 500° C. for about 1 toabout 24 hours.
 6. Method of claim 5 wherein the water-soluble acid isacetic acid.
 7. Method of claim 5 wherein the water-soluble acid isnitric acid.
 8. Method of claim 5 wherein the ratio of magnesium toaluminum is between about 2:1 to abut 3:1.
 9. Method of making2-ethyl-hexene-al comprising condensing n-butyraldehyde in the presenceof a catalyst made by mixing a water-soluble acid with pseudoboehmite toform a dispersion of pseudoboehmite crystallites, adding MgO or Mg(OH)₂in a ratio of Mg to aluminum in the gel of about 1:1 to about 10:1,agitating the mixture until the MgO or Mg(OH)₂ has substantiallydisappeared, drying the mixture, and calcining it at about 300° to about500° C. for about 1 to about 24 hours.
 10. The aldol condensation of analdehyde conducted in the presence of a catalyst made by mixing awater-soluble acid with pseudoboehmite to form a dispersion ofpseudoboehmite crystallites, adding MgO or Mg(OH)₂ in a ratio of Mg toaluminum in the gel of about 1:1 to about 10:1, agitating the mixtureuntil the MgO or Mg(OH)₂ has substantially disappeared, drying themixture, and calcining it at about 300° to about 500° C. for about 1 toabout 24 hours.